Monaghan posted three photos to Instagram, with the caption "For some people, every day is Halloween." The trio of images show the would-be Joker engaged in a dance with a character who seems to introduce a look at Jeremiah's own version of Harley Quinn.
Harley Quinn was originally created for Batman: The Animated Series, and has long stood by the Joker’s side. This unnamed character certainly seems to be similarly taken with Jeremiah.
Earlier today, the Batman prequel also released a cryptic new video on YouTube, titled "Happy Halloween from Mr. J." The 50-second clip is very Jeremiah-heavy, and loaded with Joker-heavy imagery.
We also know that the show's final season will introduce Bane, and thanks to a 10-year time jump, will finally make good on its promise to show Bruce Wayne suiting up as Batman before it wraps up for good.
Gotham will return with its final 12 episodes to the FOX Thursday night lineup on Jan. 3. Will you be watching? Let us know in the comments.